import cv2 as cv
import numpy as np
img = np.zeros((300,400),np.uint8)
step = 100
min,max = step,400
for s in range(min,max, step):
    print(s)
    img[:,0+s:min+s] = 40 + 200*s/max
threshold = 127
maxValue=255
thresholdType= cv.THRESH_BINARY
ret,thresh1=cv.threshold(img,threshold,maxValue,thresholdType)
cv.imshow('img',img)
cv.imshow('thresh1',thresh1)
cv.waitKey(0)
cv.destroyAllwindows()